Endovascular delivery devices are used in various procedures to deliver prosthetic medical devices or instruments to locations inside the body that are not readily accessible by surgery or where access without surgery is desirable. Access to a target location inside the body can be achieved by inserting and guiding the delivery device through a pathway or lumen in the body, including, but not limited to, a blood vessel, an esophagus, a trachea, any portion of the gastrointestinal tract, a lymphatic vessel, to name a few. In one specific example, a prosthetic heart valve can be mounted in a crimped state on the distal end of a delivery device and advanced through the patient's vasculature (e.g., through a femoral artery) until the prosthetic valve reaches the implantation site in the heart. The prosthetic valve is then expanded to its functional size such as by inflating a balloon on which the prosthetic valve is mounted, or by deploying the prosthetic valve from a sheath of the delivery device so that the prosthetic valve can self-expand to its functional size.
The usefulness of delivery devices is largely limited by the ability of the device to successfully navigate through small vessels and around tight bends in the vasculature, such as through the inferior vena cava or around the aortic arch. Various techniques have been employed to adjust the curvature of a section of a delivery device to help “steer” the valve through bends in the vasculature. Typically, a delivery device employs a pull wire having a distal end fixedly secured to the steerable section and a proximal end operatively connected to an adjustment knob located on a handle of the delivery device outside the body. The pull wire is typically disposed in a pull-wire lumen that extends longitudinally in or adjacent to a wall of the delivery device, for example, a sheath or catheter. Adjusting the adjustment knob, for example, rotating the knob, applies a pulling force on the pull wire, which in turn causes the steerable section to bend.
A drawback of many guide sheaths is that they are prone to undesirable deformation when deflected or flexed. For example, a guide sheath subject to significant curvature, such as when accessing the mitral valve in a transseptal approach, may kink at one or more locations along the radius of curvature, dramatically reducing the inner diameter of the guide sheath and resulting in unpredictable movement of the distal end of the guide sheath. A flexed guide sheath may also “pancake,” in which the cross-section of the catheter is ovalized due to a lack of adherence between the materials of adjacent layers of the sheath. Additionally, a flexed guide sheath may be reduced in length, or foreshortened, due to axial compression of the shaft as it is flexed. Such deformation of the guide sheath, especially at the distal end, can interfere with the precise positioning of an implant at the treatment site. Thus, a need exists for improved steerable shaft devices.